The present invention generally relates to a motor control apparatus for controlling a motor for selectively driving two mechanisms, and more particularly to a motor control apparatus for controlling a motor for selectively driving two mechanisms in which both of the mechanisms can be accurately driven.
In general, a facsimile set has a reading system for reading a image formed on a document sheet and a recording system for recording received image information on a recording sheet, and both the reading system and the recording system respectively have a driving motor for driving a mechanism for feeding the document sheet or the recording sheet. However, in a small sized facsimile set, such as a note-sized facsimile set, if both the reading system and the recording system have a motor, it is difficult to make a body thereof small and the cost thereof increases.
Thus, a facsimile set in which both the reading system and the recording system are driven by one motor has been developed for practical use. This type of facsimile set has, for example, a driving system as shown in FIG. 1.
Referring to FIG. 1, the reading system has a feed roller 3 for feeding a document sheet 2 and a one way clutch 4. The feed roller 3 presses the document sheet 2 on the surface of a contract type optical sensor unit 1 and feeds the document sheet 2 in a feeding direction indicated by an arrow. The one way clutch 4 having a gear 4a is mounted on a shaft 3a of the feed roller 3. The one way clutch 4 transmits a driving force to the shaft 3a of the feeding roller 3 so that the feeding roller 3 is rotated in only a counterclockwise direction (CCW). When the feeding roller 3 is rotated in the counterclockwise direction (CCW), the document sheet 2 is fed in the feeding direction by the feeding roller 3. The recording system has a feed roller 7 for feeding a thermal recording sheet 6 and a one way clutch 8. The feed roller 7 presses the thermal recording sheet 6 on a thermal head unit 5 and feeds the thermal recording sheet 5 in a feeding direction indicated by an arrow. The one way clutch 8 having a gear 8a is mounted on a shaft 7a of the feed roller 7. The one way clutch 8 transmits a driving force to the shaft 7a of the feed roller 7 so that the feed roller 7 is rotated in only a counterclockwise direction (CCW). When the feed roller 7 is rotated in the counterclockwise direction (CCW), the thermal recording sheet 6 is fed in the feeding direction.
A stepping motor 9 can be rotated in both the clockwise direction (CW) and the counterclockwise direction (CCW). A gear 10 is mounted on a shaft 9a of the stepping motor 9, and the gear 10 engages with a main gear 11. An intermediate gear 12 is provided between the main gear 11 and the gear 4a of the one way clutch 4 and engages with both the gears 11 and 4a. The gear 8a of the one way clutch 8 directly engages with the main gear 11.
In addition, a document sensor 13 for detecting the document sheet 2 which is supplied to the contact type optical sensor unit 1 is provided close to the contact type optical sensor unit 1.
In the above driving system, when the stepping motor 9 is rotated in the clockwise direction (CW), the gear 10 is rotated in the same direction (CW), the main gear 11 is rotated in the counterclockwise direction (CCW) and the intermediate gear 12 is rotated in the clockwise direction (CW). Then, the gear 4a of the one way clutch 4 is rotated in the counterclockwise direction (CCW), so that the one way clutch 4 transmits the driving force based on the rotation of the gear 4a in the counterclockwise direction (CCW) to the shaft 3a of the feed roller 3. Therefore, the feed roller 3a feeds the document sheet 2 in the feeding direction. At this time, the gear 8a of the one way clutch 8 is rotated by the main gear 11 in the clockwise direction (CW), so that the one way clutch 8 does not transmit the driving force based on the rotation of the gear 8a in the clockwise direction (CW) to the shaft 7a of the feed roller 7. Therefore, the feed roller 7 is not rotated and the thermal recording sheet 5 is not fed.
On the other hand, when the stepping motor 9 is rotated in the counterclockwise direction (CCW), the gear 10 is rotated in the counterclockwise direction (CCW), the main gear 11 is rotated in the clockwise direction (CW) and the gear 8a of the one way clutch 8 is rotated in the counterclockwise direction (CCW), so that the one way clutch 8 transmits the driving force based on the rotation of the gear 8a in the counterclockwise direction (CCW) to the shaft 7a of the feed roller 7. Therefore, the feed roller 7 feeds the thermal recording sheet 5 in the feeding direction. At this time, the intermediate gear 12 engaging with the main gear 11 is rotated in the counterclockwise direction (CCW), so that the gear 4a of the one way clutch 4 is rotated in the clockwise direction (CW). Therefore, the one way clutch 4 does not transmit the driving force based on the rotation of the gear 4a in the clockwise direction (CW), so that the document sheet 2 is not fed.
In the above facsimile set, when the stepping motor 9 is rotated in the clockwise direction (CW), only the feed roller 3 for feeding the document sheet 2 is driven. On the other hand, when the stepping motor 9 is rotated in the counterclockwise direction (CCW), only the feed roller 7 for feeding the thermal recording sheet 6 is driven.
Accordingly, in this facsimile set, the stepping motor 9 can selectively drive the feed roller 4 for feeding the document sheet 2 and the feed roller 7 for feeding the thermal recording sheet 5, so that it is possible to make the driving mechanism in both the reading system and the recording system simple and to decrease the cost of the facsimile set.
However, the conventional facsimile set described above has the following disadvantage.
For example, when the stepping motor 9 is rotated in the counterclockwise direction (CCW), a lower side surface of each gear tooth of the gear 10 provided on the stepping motor 9 and an upper side surface of each corresponding gear tooth of the main gear 11 are in contact with each other so that there is a gap between an upper side surface of each gear tooth of the gear 10 and a lower side surface of each corresponding gear tooth of the main gear 11. A backlash caused by this gap occurs between the gear 10 and the main gear 11. Thus, when the stepping motor 9 is reversed, from the counterclockwise direction (CCW) to the clockwise direction (CW) or from the clockwise direction (CW) to the counterclockwise direction (CCW), the driving force can not be transmitted from the gear 10 provided on the stepping motor 9 to the main gear 11 until the stepping motor 9 is rotated at an angle corresponding to the backlash. The backlash is also generated between other pairs of gears, such as main gear 11 and the intermediate gear 12, the intermediate gear 12 and the gear 4a of the one way clutch 4, and the main gear 11 and the gear 8a of the one way clutch 8, which engage with each other. As a result, when the stepping motor 9 is reversed, the stepping motor 9 is idled at an angle corresponding to the backlash. When the stepping motor 9 is idled, either the feed roller 3 for feeding the document sheet 2 or the feed roller 7 for feeding the thermal recording sheet is not rotated.
A controller controls the stepping motor 9 so that the stepping motor 9 is driven in steps corresponding to the length in which either the document sheet 2 or the thermal recording sheet 5 should be fed. For example, in a case where the length which the document sheet 2 should be fed is constant, the stepping motor 9 is driven in constant steps corresponding to the above length without regard to whether or not the stepping motor 9 is reversed. Therefore, for example, in a case where image information on the document sheet 2 is transmitted immediately after received image information is recorded on the thermal recording sheet 5, the stepping motor 9 is idled at an angle corresponding to the backlash, so that the length in which the document sheet 2 is actually fed decreases. Thus, there is a case where the document sheet 2 can not be correctly read by the contact type optical sensor 1.
In general, in a case where one motor selectively drives any two mechanisms by controlling the rotating direction of the motor, there is the same disadvantage as the above case involving the above described two mechanism.